Accuracy estimation for simplified techniques of composite structures ply-by-ply calculation method

In order to apply the standard ply-by-ply method for calculation of composite structures, a complete set of elastic characteristics of the material must be determined, which involves a lot of methodological difficulties. In the present work some methods of elastic constants approximate estimations for composite monolayers and symmetric pairs of layers, used, in particular, for creation of pressure vessels, are considered. The error of restoring the material elastic constants on the basis of the known larger Young’s modulus is determined. It was found that this error, in addition to the degree of composite anisotropy, is significantly influenced by the variation of experimental data in the used sample of composites of this class (carbon fiber-reinforced plastics (CFRP), glass fiber-reinforced plastics (GFRP) or organic fiber-reinforced plastics (OFRP)), which should be taken into account in the calculations. These conclusions are illustrated on verification stress computations in the ply pairs of a composite wound pressure vessel. A comparison of the results of ply-by-ply calculations using the full set of elastic constants and using an approximate estimation of the elastic constants via elastic modulus transformation invariants is presented. It is shown that for strongly anisotropic composite materials such as carbon fiber-reinforced plastics, in which the modulus along the fibers significantly exceeds the other elastic constants, approximate methods make it possible to carry out calculations of composite structures with acceptable accuracy without resorting to complicated computational procedures.